1. Make sure you have an USERID 11 and an ASSIGNMENT ID 24. If not, change the numbers accordingly.
2. Make sure in this course are several students (not just USER ID 11)
3. Open this link:
http://mymoodle/im/mod/assign/view.php?id=24&action=grade&rownum=0&userid=11
4. You will enter the grading form of USERID 11 and ASSIGMENT ID 24.
5. Grade the student, enter feedback, save changes.

In the next screen you will see that you did not grade USERID 11, but you graded the student in the toprow (ROWNUMBER 0?)